The various factors which are potentially capable of contributing to overall regulation of cardiovascular function during arterial hypoxia, such as vasoconstriction and vasodilation, have been studied in isolation and are relatively clearly defined. However, the extent to which these factors interact to control the distribution of tissue perfusion to the various parallel vascular circuits has received little attention. We have developed an awake dog preparation in which it is possible to repetitively standardize regional blood flow responses to arterial hypoxia with and without chemoreceptor control of the circulation. It is our intent to study regional flow with emphasis on cerebral and splanchnic hemodynamics, coronary flow and cardiac dynamics, and pulmonary hemodynamics in these animals before and after chemoreceptor denervation. The objective will be to delineate the relative roles and interactive relationships of neural and local vascular mechanisms concerned in overall regulation of the circulation during systemic hypoxia. The above studies will be coupled with chemoreceptor perfusion studies in anesthetized animals designed to obtain direct correlative data as to involvement of chemoreceptors and accessory mechanisms in control of regional flow. The long range goal will be to apply systems analysis techniques to describe the behavior of the circulation during the hypoxia responses in terms of existing models of the circulation.